1. Field of the Invention
The purpose of this invention is to provide 1) sodium silicate (water glass) impregnated wood materials introducing a fire retardant property to wood products, 2) water glass impregnation of other materials, such as paper and cloth, in such a way as to allow their intended functions while reducing the risk of flammability, and 3) wood products treated with sodium silicate can be used simultaneously to impart flame resistant properties to wood and to cause the wood to become termite resistant, providing an environmentally friendly method for long term termite control.
Liquid sodium silicate (water glass), applied to the surface of various products, can impart fire retardant properties. In the presence of fire, the sodium silicate will form foam-like crystals that help to provide an insulating barrier between the product and the flame, and will thus slow down the spread of fire. Wood and other products will become less flammable when treated with sodium silicate. The foam-like product appears to be more than a mere change in form of the sodium silicate. It is believed that the foam-like material is the product of a chemical reaction, and also imparts fire retardant properties to the material treated with sodium substrate.
It is a further purpose of the invention to provide a polymerized form of sodium silicate that is water insoluble: As a result of the application of heat, the sodium silicate undergoes dehydration (loss of water) and a process of polymerization that forms increasingly larger moieties of (SiO4)nxe2x88x921 while still maintaining an overall charge of xe2x88x921 that forms an association with the free sodium. As the material polymerizes the resultant material increases in size to the point that it is no longer able to dissolve in water, thus becoming insoluble.
Wood products, specifically wood commonly used in construction including 1xe2x80x3xc3x974xe2x80x3xc3x9712xe2x80x3 pine and composite wood materials, such as plywood, were treated with different concentrations of sodium silicate xe2x88x9240% (Na2O.SiO2) also known as water glass to test the hypothesis that water glass would make these products flame retardant. Water glass is readily available, is relatively cheap and virtually non-toxic. It can be applied to wood at industrial wood-preserving operations and can be easily applied to the homeowner. The sodium silicate will enter the voids in the wood, and harden into glass.
Cellulosic materials including dimension lumber, plywood, particle board, wafer board, paper, and fabric were treated with sodium silicate (Na2O.SiO2) in concentrations ranging from 400-0.04 g Na2O.SiO2/kg water and the surfaces of selected samples were further treated with silicon monoxide (SiO), applied in a molecular layer by vapor deposition. Tests were conducted to determine the effectiveness of these materials in terms of fire resistance, durability, duration of effectiveness, and moisture resistance.
Sodium silicate treated samples were further treated by the deposition of a molecular coating of silicon monoxide by vapor deposition. Samples treated by this technique were found to be completely moisture resistant. The combined application of sodium silicate and silicon monoxide was found to provide a fire retardant product that is moisture resistant and decomposition resistant, and therefore effective for internal and external uses. Sodium silicate coated with a thin layer of silicon monoxide does appear to provide an effective fire retardant material.
The purpose of this invention is also to provide 1) sodium silicate (water glass) impregnated wood materials will introduce a fire retardant property to wood, paper and cloth products, 2) the chemical and physical alternations of wood and other samples impregnated with sodium silicate, 3) the effects of moisture, air, temperature fluctuations, and weathering on sodium silicate treated samples, and 4) silicon oxide applied as a micro-layer to the surface of sodium silicate treated materials as an effective moisture barrier and guard against long term deterioration.
Liquid sodium silicate (water glass), applied to various products, can impart fire retardant properties. In the presence of fire, the sodium silicate will form foam-like crystals that help to provide an insulating barrier between the product and the flame, and will thus slow down the spread of fire.
In addition the sodium silicate penetrates the interiors of porous materials altering cellular structures and forming many microscopically thin glassy layers. A micro-layer of silicon oxide applied to the surface of a sodium silicate-treated material will make the material waterproof as well as prevent long term deterioration.
This invention provides impressive fire retardant properties for sodium silicate treated samples that would make this material all that would be desired in a fire retardantxe2x80x94highly effective, water insoluble, providing strengthening properties, and economical.
A further purpose of this study is to apply sodium silicate solutions to various samples for the purpose of evaluating the fire retardant properties of the resultant products. In the presence of fire, it is anticipated that the presence of non-combustible sodium silicate will render the cellulosic material less available to the flame and will retard vaporization of the cellulosic material; also sodium silicate is expected to form foam-like crystals that help to provide an insulating barrier between the product and the flame which will further separate the sample and the fire source, helping to reduce the temperature of the sample thus slowing down the spread of fire.
Sodium silicate is defined as water soluble (Condensed Chemical Dictionary, 1971). However, during pilot studies, it was noticed that as sodium silicate is exposed to large amounts of heat, parts of sodium silicate buildup would foam up, and this foam was water insoluble. This raised questions about the effect that excessive heating was having on sodium silicate. It was also noticed that when sodium silicate treated wood was subjected to heat from a flame torch, the flame was an orange/yellow color, as opposed to the light yellow traditional color of untreated wood burning. Two kinds of experiments were devised to examine the changes in sodium silicate that occur during exposure to intense flame and heat in the presence of wood. The first test was to examine water solubility versus temperature. The solubility of sodium silicate was measured after being exposed to different temperatures. The second test utilized an x-ray photoelectron spectrometer to examine the chemical composition of foamed sodium silicate byproducts.
Sodium silicate was expected to penetrate the interior of porous materials, altering cellular structures and forming many microscopically thin glassy layers. It is anticipated that the presence of sodium silicate was evident microscopically, and that the distribution patterns and interaction with cellular structures were discernible.
Products treated with sodium silicate were tested for durability, strength, and ability to withstand the effects of prolonged exposure to air, moisture, and weathering.
2. Description of the Related Art
Throughout history, house fires have been a major threat to the well-being of many families. According to the National fire Protection Association, in the United States in 1995 there were 600,000 structural fires in homes and businesses, causing approximately $7,620,000,000 in damages to property. The average loss per fire was $12,700. Over 30,000 people were injured in fires; there were 4585 deaths (12-13 per day) due to fire.
The possibility of awakening to the spectre of threatening flames strikes fear in the hearts of many, including this author, who was awakened to the acrid smell of smoke early on the morning of Jan. 26, 1995. An electrical fire in the garage had spread to nearby materials and had become a raging inferno before being discovered by a family member. The damage in this fire approached $150,000, but fortunately the effects on health were limited to a minor case of smoke inhalation. Unmeasured is the lingering fear, the memories of billowing smoke and fire, and the uneasy knowledge that it could and just might happen again, and that next time the damages might not be limited to property.
In spite of years of research, the United States remains the leader among developed nations in the number of fires occurring per year, the number of injuries and lives lost to fire, and total dollar value of property losses due to fire. The injuries and losses of life due to fire are highest among the elderly (more than double the average population), the infirm and among children. In spite of efforts to the contrary, the monetary damages, numbers of injuries and loss of life are likely to increase substantially in the future.
Fires occur in homes and business largely because of the flammability of the materials of construction and the large quantities of flammable materials placed in homes, offices and other buildings. Fires frequently start with a small flame or a spark that may last only a few seconds. The flames grow because this quick release of energy ignites nearby materials that are readily flammable especially when there is an ample supply of air. The flames then spread to other materials and grow in size and heat intensity. As the temperature increases the kindling temperature of other less flammable materials is reached and they can ignite suddenly causing the fire to spread quickly.
In recent years due to increasing costs for wood, there have been majors changes in the type of wood used in home construction. Historically, solid wood products were used as primary building materials in homes, for example 2xc3x974""s and 1xc3x974""s were used for framing, and rough wood planks were used for sub flooring and roofing support structures. The trend over the past several years has been to convert more and more from solid materials to composite materials. This is due to decreased costs for composite materials, and to the fact that many composite materials have advantages of lighter weight, less warping and increased strength. In the rush to convert to composite materials, properties related to flammability may not have received due consideration.
FIG. 1 compares weight loss profiles of 2xc3x974 dimension lumber, 1xc3x974 dimension lumber, 1xc3x974 pressure treated pine, roofing shingles, plywood, pressed wood and wafer board samples. All samples were 30 cm in length, and were tested in a chamber in which two propane torches were applied to the bottom surface of each sample according to the procedures described elsewhere in this paper.
The data show that 2xc3x974 samples exhibited the slowest rates of burn and the lowest weight loss of all samples tested. Although 2xc3x974 lumber [10] definitely will burn, the combined effects of two torches applied indefinitely was insufficient to cause a 30 cm sample to ignite and burn spontaneously. All other samples [11-16] ignited and burned readily; however, 1xc3x974 pressure treated pine [11] and 1xc3x974 untreated dimension lumber [12] generally showed slower times for ignition and lower combustion rates that the remaining samples [13-16] as follows: [13] particle board, [14] plywood, [15] shingle, and [16] wafer board.
Data listing ignition times and combustion rates is presented in Table 1 and in FIG. 2. The data for wafer board, shingles and plywood was particularly important because the steep slope of the weight loss profiles for these samples indicated that between 20 and 70 percent of these samples were burned per minute. Plywood (70%/min) is the material of choice in most homes for subflooring, subroofing and occasionally in walls of homes. Wafer board is becoming increasingly popular as a structural material, replacing 2xc3x974""s and 4xc3x974""s. Each of these three materials was completely consumed in 2-6 minutes in the standard fire tests conducted. In FIG. 2 [17] represents the results of combustion duration (min) for 2xc3x974 lumber; the test was stopped at 60 minutes. in the sample only, combustion was incomplete. In FIG. 2 [18] indicates that spontaneous burning did not occur in the 2xc3x974 lumber sample.
Currently, new homes are frequently constructed with sub floors, sub roofs, and all structural components incorporating plywood and wafer board, highly flammable materials that burn at a rate 13 to 45 times greater than that of 2xc3x974 dimension lumber.
There is therefore a need to identify building materials that provide the desired construction-properties and yet decrease the flammability of the materials to below that of 2xc3x974 dimension lumber. There is also a need to increase the fire retardant properties of furniture, fabrics, paper and other combustible materials that are stored inside structures.
Materials to be made resistant to fire in the present studyxe2x80x94wood, wood composites, paper and fabricxe2x80x94are primarily natural polymers. As has been demonstrated above, these substances vary in flammability due to the nature of the polymers, and the density and particle size of the substance, eg 2xc3x974 very dense with large particle sizes, and loosely woven fabricxe2x80x94low density with small particle sizes.
The major problems preventing widespread use of fire retardants are the costs of use, effects on physical properties of the treated materials, the water solubility of most fire retardant chemicals, making the treated samples vulnerable to leaching, and the lack of regulations requiring the use of these materials.
Based on the fact that the burn characteristics described above (FIG. 1) were obtained from samples purchased randomly in retail outlets, this investigator concluded that the fire retardants described in the literature have not yet developed attributes that are sufficiently attractive to be implemented in large scale in commercial applications in wood products. Therefore this investigator decided to search for another substance to use in fire retardant applications.
This investigator observed that sodium silicate exhibited strong adhesive properties in addition to being a noncombustible material, and theorized that the adhesive properties might be used to provide fire retardant properties in certain products. This investigator was intrigued by the fact that the possible incorporation of glass-like materials into wood and other products potentially would possibly strengthen the products as well as impart fire retardant properties.
This investigator coated small samples of wood and noticed that when the sodium silicate treated samples were applied to a flame, sodium silicate residues formed bubbles that provided a physical barrier against the flame in addition to reducing available access to flammable materials by oxygen, as heating continued the sample became incandescent. It appeared that as sodium silicate formed bubbles and droplets, the wood remained unaffected by the flame.
The idea for this invention came to me easily. My sister was using water glass to glue glass planes together to make test chambers for her science fair project. I wondered if it was possible to coat wood with water glass and help make the wood fire retardant. As I watched her work with the water glass, I played around with it and coated small pieces of wood and noticed that when the pieces were applied to a very hot flame, the water glass bubbled over forming a natural barrier against the flame. Thus, it appeared to me that as the sodium silicate formed bubbles, the wood remained unaffected by the flame.
A fire retardant material is one having properties that provide comparatively low flammability or flame spread properties (ASTM 1992). There are a number of materials that have been used to treat wood for fire retardancy including ammonium phosphate, ammonium sulfate, zinc chloride, dicyandiamide-phosphoric acid and sodium borate. Solutions of these fire-retardant formulations are effective when injected into the wood under pressure (Condensed Chemical Dictionary 1971). The sodium salts of silicon, or water glass, however, have not been identified as a fire retardant. If my hypothesis is correct, that water glass is an effective fire retardant when applied as a coating, then it could be an important finding since it is virtually non-toxic, safe to use, relatively cheap, readily available and can be easily used by the homeowner.
Sodium silicate (water glass) is a member of the family of soluble sodium silicates and is considered the simplest form of glass. The formula varies from Na2O3 SiO2 to 2Na2O.SiO2 depending on the proportions of water. The composition used in this study was a 40 percent concentration. Water glass is derived by fusing sand and soda ash; it is noncombustible with low toxicity. It is used as catalysts and silica gels; soaps and detergents; adhesives; water treatment; bleaching and sizing of textiles and paper pulp; ore treatment; soil solidification; glass foam; pigments; drilling muds; binder for foundry cores and molds; waterproofing mortars and cements; and impregnating wood. The latter use, however, has not been linked with fire retardancy (Condensed Chemical Dictionary 1971).
The terms used with flame-resistant materials are sometimes confusing. Fire resistance and flame resistance are often used in the same context as the terms fireproof or flameproof. A material that is flame resistant or fire resistant does not continue to burn or glow once the source of fire has been removed, although there is some change in the physical and chemical characteristics of the material. Fireproof or flameproof refer to material that is totally resistant to fire or flame, such as asbestos. Most organic material like wood undergo a glowing action after the flame has been eliminated. This xe2x80x9cafterglowxe2x80x9d may cause as much damage as the flaming itself.
The mechanisms of fire-retardancy are complicated. The coating theory reveals that fire resistance is due to the formation of a layer of fusible material which melts and forms a coating, thereby excluding the air necessary for the flame to propagate. This theory, first reported by Gay-Lussac in 1821, was the basis for the development of fusible salts such as carbonates, borates, and ammonium salts. The gas theory theorizes that the flame retardant produces noncombustible gases which dilutes the flammable gases. The thermal theory suggests that the flame is dissipated by an endothermic change in the retardant and the heat supplied from the source is conducted away from the wood so fast that combustion temperatures are never reached. Chemical theory says that the strong acids and bases (water glass is a strong base) impart some degree of fire retardancy (Concise Encyclopedia of Chemical Technology 1985).
My theory, and the basis for my hypothesis, is that sodium silicate can make wood and other products fire retardant. The sodium silicate will enter the voids in the wood, and harden into glass. The sodium silicate will separate the wood fibers from one another, and not allow burning. Any flame applied to the samples will not burn or spread, because it comes in direct contact with the sodium silicate. The preliminary observations I made on my own with sodium silicate and small pieces of wood showed that when in contact with a very hot flame, the sodium silicate bubbles over, forming a natural barrier against the flame and the wood remains unaffected by the flame.
To test my theory, I decided to treat (by dipping and soaking) dimension lumber with different concentrations of water glass and to burn the treated products with a propane torch to determine the potential for fire retardancy.
Dimension lumber (1xe2x80x3xc3x974xe2x80x3xc3x9712xe2x80x3 pine and 2xe2x80x3xc3x974xe2x80x3xc3x9712xe2x80x3 spruce), 1xe2x80x3xc3x974xe2x80x3xc3x9712xe2x80x3 press samples and composite materials were treated with sodium silicate by dipping (a 24-hour exposure) and soaking (a 7-day exposure) in water glass. Paper and cloth samples were similarly treated. The samples were then air dried at room temperature for a minimum of seven days. To test for fire retardancy, the wood samples were subjected to a hot flame from two propane torches for 20 minutes, and the paper and cloth samples were subjected to a candle flame. Data on flame propagation, afterglow, ash development and weight loss were collected during and after the burns. To measure variability, four replicates of each sample were burned along with an untreated sample (a control), and a sample treated with sodium borate, a known fire retardant chemical.
Samples were examined microscopically to determine characteristics of the distribution of sodium silicate within the samples. Sodium silicate-treated samples of 1xc3x974 pine, shingles, wafer board and large popsicle sticks were treated with ultra-thin layers of silicon oxide. Sodium silicate treated samples were also oven cured and were subjected to flame to convert them to glass thus imparting strength, further fire retardant properties and added strength. The samples were tested for fire retardant properties by the usual methods, for moisture resistance by exposure to boiling water and examining microscopically for evidence of sodium silicate crystals, and for strength by compression tests.
A possible solution to both the problem of moisture-related leaching and deterioration during air exposure was identified.
It was hypothesized that after being treated with sodium silicate, if a layer of silicon oxide were deposited over all surfaces, the resulting product will retain its flame retardant properties as well as be completely water proof and completely resistant to deterioration due to exposure to air or the effects of weathering. Because extraordinarily small amounts of silicon oxide would be used, the added costs would be expected to be small.
The present invention thus involves a process of imparting fire retardant properties to a cellulosic material comprising coating a cellulosic material with sodium silicate by contacting a sodium silicate solution with the material to be coated, dehydrating the coating, and depositing a coating of a silicon oxide glassy film on the sodium silicate coated material. In one embodiment, the coating of silicon oxide is a monomolecular layer of silicon.